Nerve evoked potentials are the electrical signals or responses generated by the nervous system, generally referred to as nerve action potentials, in response to stimuli. The electrical signals can be single event trials or averaged single event trials presented as an evoked response or an evoked potential. Nerve evoked potentials are considered neurophysiological representations of peripheral nerve, spinal cord, and brain function. Intra-operative neurophysiological (IONM) monitoring of such nerve evoked potentials is assessed for latency and amplitude measurements that reflect both sensory and motor nerve fiber function. Generally, such intra-operative nerve evoked potentials are well established for clinically evaluating the electrophysiological presentation in patients with neurological symptoms.
Evaluating function of the sensory nervous system during surgery has been performed since the late 1970s. Intra-operative somatosensory evoked potentials (SSEP) monitoring is used to assess the functional integrity of the sensory nervous system pathways during surgical operations that put the spinal cord or brain at risk for significant ischemic or traumatic injury. The operative team identifies the neurological region at risk and selects a sensory pathway that carries a physiological signal through that region.
Currently, placement of stimulating electrodes has been largely limited by either radiologic evidence of positioning and placement during surgery. Since most patients are under general anesthesia and unconscious, the patients cannot elicit any sensory perceptions and/or autonomic responses. As such, there is a need for observing a real time physiological response that is independent of a patient's consciousness or perceptions.